At present, proteins and other small molecules are crystallized by a variety of conventional experimental methods. Among these many methods, there are three that are most commonly used in the art. These three methods are (1) vapor diffusion methods, which decrease the solubility and concentrate the molecules to be crystallized by means of solvent evaporation. This method is often referred to as the "hanging drop technique." (2) The batch method, which decreases the solubility of the molecule by the direct addition of various precipitating agents to the solution. These precipitating agents are usually organic compounds such as polyethylene glycol, or inorganic salts such as ammonium sulphate. (3) The dialysis method, in which the protein or other molecular solution is physically isolated from the precipitating agent by a semi-permeable membrane. Upon activation, the precipitating agents diffuse through the membrane and mix with the protein solution. In general, if the other experimental factors are appropriately chosen, e.g., pH and temperature, crystallization of the protein or other molecule occurs during conditions of supersaturation.
Unfortunately, it has been observed that crystal growth and other chemical syntheses carried out under normal gravitational conditions suffer from turbulent convective flows which occur in all of the above described methods. In particular, during crystal growth under 1g the solute-depleted regions surrounding a growing crystal normally produce these turbulent convective flows which appear to have significant effects on the crystal quality. For methods such as liquid - liquid diffusion and dialysis, which require the diffusive mixing of two solutions of greatly differing densities, the elimination of these density driven convection flows is of the utmost importance if one is to successfully carry out crystal growth and other chemical syntheses.
In microgravity, i.e., low gravity environments, crystal growth and chemical syntheses can be carried out with no density driven convective flows. Under these conditions, crystal growth primarily becomes a diffusion limited process. Current research indicates that the slower approach to critical supersaturation occurring in low gravity environments reduces the number of nucleation sites created, and increases the terminal size of the crystals grown therein. The application of very slow diffusive mixing which will occur in microgravity is also advantageous in that it allows the conditions of supersaturation to be approached in a uniform gradient. As a result of lack of turbulence and very slow diffusive mixing, low gravity environments are ideal for maximizing crystal growth and successfully carrying out a variety of other chemical syntheses.
Although there are devices presently known for carrying out chemical synthesis under low gravity conditions, such as the Littke sliding seal arrangement, the Boeing dialysis device and the 3-M liquid-liquid diffusion flight hardware, there are no present devices for simply and inexpensively carrying out a large number of chemical syntheses or small molecule crystallization operations, particularly where those operations require a quench step. It is thus desirable to develop a simple device made of inexpensive materials which can carry out a large number of crystallization experiments or chemical reactions while taking advantage of the benefits of a low gravity environment.